Telecommunication systems, cable television systems and data communication networks use optical networks to rapidly convey large amounts of information between remote points. In an optical network, information is conveyed in the form of optical signals through optical fibers. Optical fibers comprise thin strands of glass capable of transmitting the signals over long distances with very low loss.
Optical networks often employ wavelength division multiplexing (WDM) or dense wavelength division multiplexing (DWDM) to increase transmission capacity. In WDM and DWDM networks, a number of optical channels are carried in each fiber at different wavelengths. Network capacity is based on the number of wavelengths, or channels, in each fiber and the bandwidth or size of the channels. Network capacity in a ring network is also limited by data processing at each node in the ring.
The topology in which WDM and DWDM networks are built plays a key role in determining the extent to which such networks are utilized. Ring topologies are common in today's networks. WDM nodes serve as network elements on the periphery of such optical rings and traditionally require optical-to-electrical conversion at each node to route data to local clients. WDM add/drop equipment at each node typically employs optical-to-electrical or electrical-to-optical conversion of each constituent channel to add, drop, or pass a channel.